Recently, electronic appliances for consumer use, such as (i) portable electronic appliances such as a mobile phone or (ii) health equipment typified by an electronic thermometer and a sphygmomanometer, face a demand for supply of a thin, light-weight, small, and highly waterproof wearable product at a reasonable price.
In general, the electronic appliances as described above are each configured by assembling various electronic components on a printed circuit board. Note here that examples of the various electronic components include (i) a passive component such as a resistor or a capacitor, (ii) an active component such as an LSI (large scale integrated circuit) or an IC (integrated circuit), (iii) a power supply such as a battery, (iv) a display such as an LED (light emitting diode), and (v) a sensor or a switch.
In general, the printed circuit board is fabricated in such a manner that copper foil is laminated on a sheet of an epoxy resin board (glass epoxy substrate) reinforced with glass fiber or on a sheet of a polyimide substrate (flexible board), and the copper foil laminated is etched so as to form a wiring circuit. Other electronic components are mounted on the wiring circuit with use of solder, a conductive adhesive, a metal wire, or the like to thereby assemble an electronic appliance.
However, the printed circuit board whose circuit is fabricated by etching the copper foil involves a high material cost and a high processing cost, and the mounting of the electronic components with use of the solder, the conductive adhesive, the metal wire, or the like also involves a high material cost and a high processing cost. This makes the electronic appliance expensive. Further, waste fluid discharged during the etching process imposes much damage on the environment.
There is another problem that mounting the electronic components on the printed circuit board requires a certain amount of space between the electronic components, and this results in an increase in thickness of a product obtained and a limitation on downsizing of the product.
To solve these problems, a method for mounting electronic components has been proposed which method uses no printed circuit board in order to achieve reductions in width, size, and cost of a product.
For example, Patent Literature 1 discloses an electronic circuit package in which an electronic component, a circuit element, and the like are embedded in a molded resin such that an electrode surface is exposed. The electronic circuit package is manufactured in the following manner. First, the electronic component, the circuit element, and the like are temporally fixed with use of thermosetting resin. Next, the electronic component, the circuit element, and the like are embedded in the molded resin by injection molding. Then, the resin used for temporally fixing the electronic component, the circuit element, and the like is removed by dissolving, so that the electrode surface is exposed. On the electrode surface thus exposed, a conductor layer is formed and then subjected to exposure and etching, so that a wiring pattern is formed. Thus, the electronic circuit package is manufactured.
Patent Literature 2 discloses a method of using, as an exterior component, a resin in which an electronic component is embedded. According to Patent Literature 2, a circuit is formed by, for example, a technique in which the electronic component is embedded in an inner surface of the resin such that an electrode of the electronic component is exposed, and then silver paste is printed. According to this, the exterior component serves as a substrate, so that no substrate for forming the circuit thereon is necessary. This enables a reduction in width of a product obtained.
Patent Literature 3 discloses an electronic component-mounted device in which an electronic component is embedded in a resin molded article. In the electronic component-mounted device, the electronic component is embedded in the resin molded article such that an electrode of the electronic component is exposed. As such, by electrically connecting the exposed electrode, it is possible to omit (i) a member (substrate) for fixing the electronic component in a state where the electronic component is positioned and (ii) an operation of assembling the electronic component onto a housing.